Referring to FIG. 1, a schematic diagram of some components contained in an inkjet printer is illustrated. The supporting pedestal 11 of the inkjet head 10 is driven by the motor 12, the gear set 13 and the belt 14 to linearly move along the gliding rod 19 back and forth. In such manner, the inkjet head 10 is moved to the desired positions for performing the printing tasks. For actually realizing the position of the inkjet head 10 by the control unit (not shown in this drawing), the optical encoder 15 which is carried on the supporting pedestal 11 generates a position feedback signal and a speed feedback signal according to the graduations of the optical ruler 16. In response to the position feedback signal and the speed feedback signal, the control unit generates a control signal to control movement of the inkjet head 10.
Please refer to FIG. 2, which is a functional block diagram illustrating the control unit of the inkjet printer. According to a computation associated with the position command value and the speed command value outputted from the path planning unit 20, the proportional-integral-differential (PID) controller 21 issues a control signal to the actuating device 22 such as the motor 2 described above. An exemplified control signal is a pulse width modulation (PWM) signal. In response to the control signal, the mechanical installation 23 including for example the gear set 13, the belt 14 and the inkjet head 10 as described above is driven by the actuating device 22. The position feedback signal and the speed feedback signal generated by the feedback unit 24, which includes the optical encoder 15 and the optical ruler 16 as described above, are fed back to the input end of the PID controller 21. According to the difference between the position command value and the position feedback signal (i.e. the position error signal) and the difference between the speed command value and the speed feedback signal (i.e. the speed error signal), the PID controller 21 issues the control signal to control the driving force of the actuating device 22.
As previously described, the control signal is generated from the PID controller 21 according to the position error signal and the speed error signal. Under this circumstance, these error signals should be large enough to generate sufficient voltage of the control signal to drive the actuating device 22. Therefore, the control unit of the inkjet printer has some drawbacks such as a slow response speed and a large speed error signal.
In views of the above-described disadvantages resulted from the prior art, the applicant keeps on carving unflaggingly to develop an actuating control device according to the present invention through wholehearted experience and research.